Cross lappers serve to lay multiple layers of a fiber web supplied by a carding machine uniformly on an output conveyor belt. The fiber web is usually sent through an upper carriage first and from there to a laying carriage, through the laying nip of which the fiber web is laid onto the output conveyor belt. To guide the fiber web through the cross lapper, at least two fiber web conveyor belts are used. The movements of the web conveyor belts, of the upper carriage, and of the laying carriage are controlled in coordination with each other.
In the area extending from the infeed area of the cross lapper to the upper carriage, it is advantageous for the fiber web not only to rest on the web conveyor belt but also to be sandwiched from above by a cover belt. The purpose of this is to prevent the fiber web from being blown about and thus to ensure the uniformity of the laid nonwoven. Structures of this type are known from DE 195 43 623 A1, EP 1 136 600 A1, and EP 1 870 499 B1, for example. The disadvantage of these cross lapper designs is the complexity with which the endless cover belt must be guided, which requires a large number of components and considerable mechanical effort.
EP 2 479 321 A1 discloses a simplified configuration of cross lapper, in which the cover belt is smooth and does not move along with the fiber web. Instead, it serves as a more-or-less stationary cover for the fiber web. To ensure that the cover belt covers the fiber web on the web conveyor belt for as long as possible, the cover belt runs from an attachment point in the infeed area of the cross lapper, through the upper carriage, to a second attachment point at the other end of the cross lapper.
The disadvantage of this configuration is that, when the cover belt slides through the upper carriage, high relative speeds are reached between the stationary cover belt and the upper carriage as it travels back and forth in the transverse direction. This results in severe stress on the cover belt and increased wear, especially in the area of the reversal point of the upper carriage.